CacyBP/SIP knockdown inhibits cell cycle process of colon cancer by suppressing CDK8-mediated Wnt/β-catenin signaling pathway

Abstract

Abstract Background Previously, we found that calcyclin-binding or siah-1-interacting protein (CacyBP/SIP) promotes colon cancer proliferation. However, the potential mechanism has not been fully revealed. Methods CacyBP/SIP nuclear translocation was induced by gastrin in the SW480 cell line and verified by the Western blotting and qPCR. The ubiquitin and cell cycle microarrays were constructed to identify the downstream target proteins of CacyBP/SIP nuclear translocation. CacyBP/SIP and CDK8 expressions were detected by the immunohistochemistry (IHC) and validated by TCGA samples. The cell distributions were analyzed by the flow cytometry. Lentivirus-mediated shRNAs were used to perform the knockdown experiments. Ubiquitin degradation pathway was inhibited by the proteasome inhibitor MG132. Results CacyBP/SIP nuclear translocation was successfully induced under gastrin treatment for 48h. Gene chip screening confirmed that CDK8 was the key downstream target protein of CacyBP/SIP in the nucleus. CacyBP/SIP and CDK8 were highly expressed in primary colon cancer tissues compared to the adjacent and normal tissues. CacyBP/SIP knockdown decreased CDK8 and β-catenin expressions, causing a cell cycle arrest at the G0/1 phase. Meanwhile, knocking down CDK8 alone can inhibit the expression of β-catenin. In addition, MG132 inhibited the E3 ligases-mediated degradation pathway, up-regulating CDK8 expression. Furthermore, Skp2 knockdown suppressed the activity of the CacyBP/SIP-formed E3 ligase (CacyBP/SIP-Siah-1- Skp1-Cullin-1-Skp2), which facilitated CDK8 degradation by other E3 ligases. Conclusion CacyBP/SIP nuclear translocation contributes to the cell cycle progression of colon cancer via CDK8-mediated Wnt/β-catenin signaling pathway. Moreover, CacyBP/SIP can through E3 ligase-mediated regulation of CDK8 expression in colon cancer.